Particularly in automotive engineering but also in other application area, such as aircraft construction or rail vehicle construction, metal sheets made from aluminium alloys are required that not only have particularly high strength values but also very good formability characteristics, and enable a high degree of deformation. In automotive engineering, typical application areas are the body and chassis parts. For visible, painted components, for example body sheet metal that is visible from the outside, the deformation of the materials must also occur in such a way that the surface is not marred by faults after painting, such as slip lines or roping. This is particularly important, for example, when aluminium alloy sheets are used to manufacture engine bonnets and other body components of a vehicle. However, it also limits the choice of material in terms of the aluminium alloy. In particular, AlMgSi alloys, the main alloy components of which are magnesium and silicon, have relatively high strengths and at the same time good formability characteristics and exceptional corrosion resistance. AlMgSi alloys are the AA6XXX alloy types, for example alloy types AA6016, AA6014, AA6181, AA6060 and AA6111. Aluminium strips are usually manufactured from an AlMgSi alloy by casting a rolling ingot, homogenising the rolling ingot, hot-rolling the rolling ingot and cold-rolling the warm strip. The rolling ingot is homogenised at a temperature from 380 to 580° C. for more than one hour. With final solution annealing and subsequent quenching and natural aging at about room temperature for at least three days, the strips can be shipped in condition T4. Condition T6 is adjusted after quenching by artificial aging at temperatures between 100 and 220° C.
It is problematic that hot-rolled aluminium strips made from AlMgSi alloys contain coarse precipitates of Mg2Si, which are broken up and reduced in size in the subsequent cold rolling due to their high degrees of deformation. Hot strips of an AlMgSi alloy are usually produced in thicknesses from 3 mm to 12 mm and then passed to a cold rolling stage with high degrees of deformation. Since the temperature range in which the AlMgSi phases are formed is passed through very slowly in conventional hot rolling, the phases produced thereby are very coarse. The temperature range for forming the phases referred to above depends on the alloy, but is between 550° C. and 230° C. It has been demonstrated experimentally that these coarse phases in the hot strip impair the elongation of the end product. This means that it has not previously been possible to fully exploit the formability characteristics of aluminium strips made from AlMgSi alloys.
The object underlying the present invention is therefore to provide a method for producing an aluminium strip from an AlMgSi alloy and an aluminium strip that has a higher elongation in the T4 state, and to this extent enables higher degrees of deformation when producing structured components for example. A further object underlying the invention is also to suggest advantageous uses for a metal sheet produced from the aluminium strip according to the invention.